I thoroughly enjoyed building Helm's Deep following the journeybook guidelines, however I do agree that they weren't the most detailed instructions. The instructions for the wall sections were fine, however in hindsight and after playing some games using the terrain, I would make the walls a bit wider.
I mostly felt that the gatehouse was fairly complete with instructions, although I did build it a while ago myself so I am a bit hazy at remembering. I had to design two parts completely myself though, the triangular wedge of stairs that leads up to the gatehouse from the deeping wall, and the ramp inside the gatehouse. However, having built everything else by that stage, those two pieces were simple enough to put together.
In terms of the height issues with the journeybook version, I do agree that it is not accurately scaled as per the movies. I both like and dislike this; I like it because it enables much easier storage, especially when combined with the fact that there are so many separate pieces for the whole Helm's Deep structure which means that there is no one-piece huge structure to attempt to store somewhere. But on the flipside, the model does lack that verticality that is pretty iconic of Helm's Deep (for me anyway).
Maybe when I get some more storage space somewhere down the line I'll attempt a more detailed build, but for now, judging by your report, it seems to be sufficient